1. Field of the Invention
The present invention relates to methods and apparatus for filling and circulating fluid through a well casing string as it is being run into a well bore, and preventing spillage of the fluid when casing joints are added to the string or the filling and circulating apparatus is otherwise removed from the casing string.
2. Description of the Prior Art
In the construction of oil and gas wells, a well bore is drilled into one or more subterranean formations or zones containing oil and/or gas to be produced. The well bore is typically drilled utilizing a drilling rig which has a rotary table on its floor to rotate a pipe string during drilling and other operations. The drilling rig may also have a top drive mechanism for rotating the pipe string which is integral with the traveling block of the rig in addition to or instead of a rotary table.
During a well bore drilling operation, drilling fluid (also called drilling mud) is circulated through the well bore by pumping it down the drill string, through the drill bit and upwardly back to the surface through the annulus between the walls of the well bore and the drill string. The circulation of the drilling fluid functions to lubricate the drill bit, remove cuttings from the well bore as they are produced and to exert hydrostatic pressure on pressurized fluid containing formations penetrated by the well bore whereby blow-outs are prevented.
In most instances, after the well bore is drilled, the drill string is removed therefrom and a string of casing is run thereinto while maintaining sufficient drilling fluid in the well bore to prevent blow-outs, etc. During casing running operations, i.e., the lowering of a casing string into the well bore, it is not uncommon for the casing string to become stuck in the well bore. In such instances, the casing is usually washed free by circulating a fluid, usually drilling fluid, down the casing and through the lower end thereof to wash sand or other debris away from the casing. Also, during casing running operations, the casing string must be kept filled with fluid to prevent excessive fluid pressure differentials across the casing string and to prevent blow-outs. Typically, fluid is added to the casing string after each additional casing joint is added to the string and the string is lowered into the well bore.
In order to fill the casing string with fluid as it is being lowered and to circulate fluid through the casing string when it becomes stuck, the upper end of the casing is sealed with a device for allowing fluid to be pumped into the casing string as it is being lowered or unstuck. An example of such a filling and circulating device is described in U.S. Pat. No. 4,997,042 issued on Mar. 5, 1991 to Jordan et al. While the Jordan et al. device and method for using the device may satisfactorily allow a casing string being run into a well bore to be filled with fluid and for the fluid to be circulated when required to prevent sticking, a problem encountered with the device and other heretofore developed and used casing filling and circulating devices involves the spillage of fluid. That is, each time a casing joint is added to the casing string, the filling and circulating device must be removed from the casing string and reinstalled in the top of the casing joint added thereto. Because the fluid pressure inside the casing string is often greater than the fluid pressure within the filling and circulating device, when the device is removed from the casing string the ensuing pressure release often causes fluid to be spilled on the rig floor which produces a safety hazard to rig personnel. The fluid pressure differential between the filling and circulating device and the casing string is brought about by a check valve included in the device to prevent back-flow of fluid as the casing string is lowered into the well bore.
Thus, there is a need for an improved casing filling and circulating apparatus and method of using the apparatus whereby a casing string can be efficiently made up and lowered into a well bore without spillage of fluid occurring.